The present invention relates to a method for manufacturing an organic Electro Luminescence (EL) display having a high resolution and excellent visibility and used for a wide range of applications such as a display of a mobile terminal or an industrial meter.
In recent years, the information technology has greatly advanced and the application of the technology has been expanding rapidly. In the field of a display device, there has been developed a high-resolution display device with a low power consumption and a high-speed response for meeting demands for mobility and displaying motion pictures.
In order to display a color image, a display device driven by a thin film transistor (TFT) has been developed. In such a device, it is difficult to provide a large opening in a system where light passes through a substrate having the TFT due to a shielding effect of a wiring portion. Therefore, there has been recently developed a top emission system in which the light radiates toward a side opposite to the substrate having the TFT.
In the top emission system, light emitting elements for the primary colors, i.e. red (R), green (G) and blue (B), are arranged separately in a matrix. Therefore, it is necessary to precisely arrange light emitting materials for the RGB over the matrix. Accordingly, it is difficult to manufacture such a system efficiently at a low cost. Moreover, the three light emitting materials have different luminescence characteristics and driving conditions. Therefore, it is still very difficult to obtain good color reproducibility for long time.
In a system where a backlight emits white light and a color filter is used to obtain the three primary colors, it is difficult to improve efficiency of the white backlight.
In a system called a color conversion system, fluorescent materials are arranged separately and absorb excited light so that the individual fluorescent element emits fluorescent light in multiple colors. It is perceived that only the color conversion system can provide a high-resolution and bright organic EL display with a combination of the top emission method using the TFT drive system. Japanese Patent Publications (Kokai) No. 11-251059 and No. 2000-77191 have disclosed such color display devices.
FIG. 6 is a view showing a structure of a conventional organic EL display. As shown in FIG. 6, TFTs 604, anodes 606, an organic EL layer 608 and a cathode 610 are formed on a substrate 602. A color conversion filter layer 612 and a black mask 614 are formed on a transparent substrate 616. An outer sealing wall 618 formed of a room temperature setting two-part epoxy adhesive is formed around a periphery of the substrate 602 to adhere to the transparent substrate 616. An internal space 620 is formed between the two substrates. In general, it takes long time, i.e. 24 hours, to cure the outer sealing wall 618 at the room temperature. Therefore, it is necessary to hold the device during the curing at the temperature after the anodes 606 and the color conversion filter layer 612 are positioned, so that the device is not shifted.
In the color display using the color conversion filter layer shown in FIG. 6, it is necessary to obtain a function of displaying high-resolution colors. The organic EL element needs to have long-term stability including the color reproducibility. A device needs to have a simple configuration and sealing structure to reduce time for manufacturing.
In the organic EL display shown in FIG. 6, it is necessary to accurately position (or align) the color conversion filter layer 612 and the anodes 606. An adhesive for the outer sealing wall 618 needs to remain stable without any state change such as a viscosity change or a gelation until the alignment is completed, so that the alignment can be adjusted freely. On the other hand, the adhesive needs to be cured in a short period of time once the alignment is completed.
In the organic EL display shown in FIG. 6, the internal space 620 is formed between the two substrates. As a result, the light emitted from the organic EL layer 608 is reflected at an interface between the internal space and the cathode, and at an interface between the internal space and the color conversion filter layer due to a large difference in refractive indexes. In order to solve this problem, it is possible to fill a transparent material with a high refractive index in the internal space 620. In this case, however, the transparent material filled in the internal space 620 contacts the adhesive of the outer sealing wall 618 before the adhesive is cured, thereby preventing the adhesive from curing completely.
In view of the aforementioned problems, the present invention has been conceived, and an object of the invention is to provide an organic EL display and a method of producing the organic EL display, in which a transparent material filled in an internal space does not contact an adhesive used for an outer sealing wall to prevent an insufficient curing of the outer sealing wall. It is also possible to precisely position (align) a color conversion filter layer and anodes, and to set the outer sealing wall promptly.
Another object of the invention is to provide a sealing structure and a sealing method for an organic EL display, in which light from an organic EL layer effectively transmits to a color conversion filter layer without reflecting inside the device, so that stable light emitting characteristics can be maintained over a long period of time while preventing moisture or the like from outside.
Further objects and advantages of the invention will be apparent from the following description of the invention.